of the antenna will not be possible with this geometry. The rectangular high hat design is not an attractive structural geometry but does offer an improved temperature picture. The triangular hat design has the lowest maximum temperature level and minimum gradient of the concepts considered. Aluminum construction of the tri-beam horizontal members can be considered with this cross section. The temperature profiles along the horizontal structural tri-beam caps were evaluated for various orbital positions during the equinoxes and solstices. Figure 2-17 presents the expected variation in thermal gradients between primary and secondary structural caps. The average primary structure thermal gradient is approximately at the center of the antenna. The expected variation in this gradient is . The thermal gradients between secondary structural caps are small, , and do not present a significant thermally induced deflection environment. The vertical columns of the structure have the same view of the antenna surface and space, and consequently cannot be readily configured with coatings, insulation or geometry selection to minimize peak temperatures of the material. Figure 2-18 presents the maximum waste heat flux that will be experienced by the vertical columns for microwave converter efficiency of and . Eighty-seven percent of the waste heat generated by the converters is assumed radiated toward the structure. The parameter p is a scaling factor for the shape of the Gaussian distribution of microwave converters on the antenna surface. Limitations as to the taper of this distribution must be imposed depending upon the structural material selected. A near uniform distribution (1. 5 to 1) must be used if the structure is aluminum or graphite/epoxy (70% converter efficiency). Selection of graphite/polyimide would be compatible with a desirable 10:1 taper for the converter Gaussian distribution. 2. 2. 3. 2 Structural Analysis The Task 2 structural analysis objective was to refine the design of the structural members and to perform a detailed assessment of thermally induced deflections. The following summarizes these assessments: • The principal applied load for structure design is that induced by inertial response of the control system during breakaway from the slip-ring torque. This torque equates to a 100 lb (440N) end load on the upper and lower members.
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